The field of the invention is heavy equipment for surface mine field loading operations such as power shovels, drag lines, and the like, and more particularly to systems used on such equipment to measure the net weight of material in each load.
In large scale surface mining operations, equipment of immense proportions is used to load and transport material. Loading is usually performed by power shovels with a bucket capacity of about 40 tons per scoop. Equally mammouth trucks are loaded with the material and haul it to a processing location. The largest trucks have a capacity of about 235 tons.
Overloading the trucks can lead to premature fatigue and failure causing excessive maintenance costs. Without a measurement of the actual weight of material in the truck, the power shovel operator can only guess the weight based on an extremely rough estimate of the volume of material in the truck. Therefore, to prevent chronic overloading, the trucks are routinely underloaded. But such underloading can cause significant loss of production.
Measurement systems have been developed to indicate the net weight of material in the power shovel bucket as it is transferred to the truck. Due to the massive size of the equipment involved, it is not practical to instrument the power shovel with strain gauges and the like. Rather, prior measurement systems function by first sensing the electrical load of the power shovel drive motors, then computing the motor torque based on that electrical load, and finally computing an estimate of the net weight based on the motor torque, the known power shovel geometry, and the known tare weights.
Although such measurement systems have been constructed and used, they have been ineffective due to large inaccuracies in the measurements on the order of .+-.20% or more. These errors stem from the fact that the existing measurement systems do not account for the complex dynamic operation of such enormous equipment. Therefore, measurements are not only in error, but are erratic and unpredictable. In order to be effective, a measurement system would have to be capable of accurately and repeatedly performing measurements to within a small error, .+-.2% for example. Otherwise, the problems of overloading and underloading would persist. Existing systems have neither approached the needed accuracy nor repeatability.
It is an advantage of the present invention to provide an improved system for measuring the load weight of large mining and lifting machinery.
It is another advantage of this invention to provide a measuring system of the foregoing type which effects calculations of load weights while in a dynamic state.
It is still another advantage of this invention to provide a measuring system of the foregoing type which can determine such calculations in a dynamic state and with an accuracy of within .+-.2%.
It is yet another advantage of the present invention to provide a measuring system of the foregoing type which is adaptable for use with a wide variety of mining and lifting machinery.
It is still another advantage of this invention to provide a measuring system of the foregoing type wherein the need to recalibrate sensing devices which might otherwise be used.